More Practical THz Imaging on the Horizon

CAMBRIDGE, Mass., May 6, 2014 — A new theory offers to reduce the number of sensors required for high-resolution terahertz and millimeter-wave imaging, potentially making the techniques more practical.

Traditional terahertz imaging compares measurements across a dense array of sensors, the distance between them proportional to wavelength, to produce images. The new technique, developed by a team from the MIT Research Laboratory for Electronics, involves increasing the space between sensors and using fewer of them.

As long as the distance between sensors is no more than half the length of the incoming wave, the calculation is a fairly straightforward matter of inverting the sensors' measurements.

However, if the sensors are spaced farther than half a wavelength apart, the inversion will yield more than one possible solution. Those solutions will be spaced at regular angles around the sensor array in a process known as spatial aliasing.

The researchers advocate for a detector that distributes sensors in pairs within a uniform distance of each other to ensure efficient calculation of the scene reconstruction, while also maintaining an irregular distance between the pairs.

“In this architecture,” the researchers wrote in their paper, “the array elements are configured in a periodic nonuniform pattern that can be viewed as the superposition of multiple sparse uniform subarrays.”

The researchers have also developed an algorithm that determines the optimal pattern for the sensors' distribution. This maximizes the number of different distances between pairs.

“Think about a range around you, like five feet,” said Dr. Gregory Wornell, the Sumitomo Electric Industries professor of engineering in MIT's Department of Electrical Engineering and Computer Science. “There's actually not that much at five feet around you…or at 10 feet. Different parts of the scene are occupied at those different ranges, but at any given range, it's pretty sparse.”

He added that if 10 percent of the scene at a given range is occupied, “only 10 percent of the full array [is needed] to still be able to achieve full resolution.”

The new technique could support the design of new, high-resolution radar and sonar systems, as well as in airport security, explosives detection and collision avoidance, researchers said.